Little is known about the mechanisms of change in cognitive behavioral therapy (CBT) for anxious youth, potentially because most treatment outcome studies have focused only on changes in diagnostic status and symptoms, rather than using a multi-method approach to understand changes across multiple systems associated with recovery. Using a transdisciplinary approach, this core will provide an integrated structure for examining changes in symptoms, behavior in family and peer contexts, sleep, and brain reactivity to cognitive and emotional information processing tasks among anxious children before, during, and after CBT and CCT. These data will be used as the basis for analyses across all three of the primary projects. Specifically, this core describes the following assessments. Before and after treatment, participants will complete measures of clinical status, symptoms, affective style, and parent-child interactions using rating scales, self-report measures, and behavioral observations. Genetic data will also be acquired. Participants will complete cognitive and affective information processing measures during fMRI and concurrent pupil dilation/eyetracking assessment, as well as event-related potential (ERP) assessment. On a biweekly basis throughout treatment, participants will complete self-report ratings of symptomatology, pupil dilation/eyetracking assessments, and a home based Ecological Momentary Assessment and sleep actigraphy protocol. This core integrates and oversees the assessment methodologies for all projects. Of particular importance, methods are provided for creating composite summary indices for each primary domain of assessment, for use in each project and in cross-project analyses, via methods developed in Core 3. Having these methods centralized in a single core, with a single project coordinator, and an integrative measurement approach is essential for this CIDAR mechanism. Centralizing the administration of these assessments will 1) contribute to a better understanding of how these assessments fit together, 2) facilitate later integration of analyses and results across projects, and 3) increase efficiency and decrease participant burden by integrating assessments in a convenient and planful manner.